Name

glLinkProgram — Links a program object

C Specification

void glLinkProgram(

GLuint program);

Parameters

program

Specifies the handle of the program object to be linked.

Description

glLinkProgram links the program
object specified by program. Shader objects
of type GL_VERTEX_SHADER attached to
program are used to
create an executable that will run on the programmable vertex
processor. Shader objects of type GL_FRAGMENT_SHADER
attached to program are used to create an
executable that will run on the programmable fragment
processor.

The status of the link operation will be stored as part of
the program object's state. This value will be set to
GL_TRUE if the program object was linked
without errors and is ready for use, and
GL_FALSE otherwise. It can be queried by
calling
glGetProgramiv
with arguments program and
GL_LINK_STATUS.

As a result of a successful link operation, all active
user-defined uniform variables belonging to
program will be initialized to 0, and
each of the program object's active uniform variables will be
assigned a location that can be queried by calling
glGetUniformLocation.
All active uniforms belonging to the program’s named uniform blocks are
assigned offsets (and strides for array and matrix type uniforms) within
the uniform block. Also, any active user-defined attribute variables that have not
been bound to a generic vertex attribute index will be bound to
one at this time.

Linking of a program object can fail for a number of
reasons as specified in the OpenGL ES Shading Language
Specification. The following lists some of the
conditions that will cause a link error.

A vertex shader and a fragment shader are not both
present in the program object.

The vertex and fragment shader do not use the same
shader language version.

The number of active attribute variables supported
by the implementation has been exceeded.

The storage limit for uniform variables has been
exceeded.

The number of active uniform variables supported
by the implementation has been exceeded.

The main function is missing
for the vertex or fragment shader.

A varying variable actually used in the fragment
shader is not declared in the same way (or is not
declared at all) in the vertex shader.

A reference to a function or variable name is
unresolved.

A shared global is declared with two different
types or two different initial values.

One or more of the attached shader objects has not
been successfully compiled (via glCompileShader)
or loaded with a pre-compiled shader binary
(via glShaderBinary).

Binding a generic attribute matrix caused some
rows of the matrix to fall outside the allowed maximum
of GL_MAX_VERTEX_ATTRIBS.

Not enough contiguous vertex attribute slots could
be found to bind attribute matrices.

The total number of components to capture in any transform feedback varying variable
is greater than the constant GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS
and the buffer mode is GL_SEPARATE_ATTRIBS.

The total number of components to capture in any transform feedback varying variable
is greater than the constant GL_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS
and the buffer mode is GL_INTERLEAVED_ATTRIBS.

When a program object has been successfully linked, the
program object can be made part of current state by calling
glUseProgram.
Whether or not the link operation was successful, the program
object's information log will be overwritten. The information
log can be retrieved by calling
glGetProgramInfoLog.

glLinkProgram will also install the
generated executables as part of the current rendering state if
the link operation was successful and the specified program
object is already currently in use as a result of a previous
call to
glUseProgram.
If the program object currently in use is relinked
unsuccessfully, its link status will be set to
GL_FALSE , but the executables and
associated state will remain part of the current state until a
subsequent call to glUseProgram removes it
from use. After it is removed from use, it cannot be made part
of current state until it has been successfully relinked.

The program object's information log is updated and the
program is generated at the time of the link operation. After
the link operation, applications are free to modify attached
shader objects, compile attached shader objects, detach shader
objects, delete shader objects, and attach additional shader
objects. None of these operations affects the information log or
the program that is part of the program object.

Notes

If the link operation is unsuccessful, any information about a previous link operation on program
is lost (i.e., a failed link does not restore the old state of program
). Certain information can still be retrieved from program
even after an unsuccessful link operation. See for instance glGetActiveAttrib
and glGetActiveUniform.

Errors

GL_INVALID_VALUE
is generated if program
is not a value generated by OpenGL.

GL_INVALID_OPERATION
is generated if program
is not a program object.

GL_INVALID_OPERATION
is generated if program is the currently active program
object and transform feedback mode is active.